The release of 2,4,5-trichlorophenol (2,4,5-T) containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at Sèveso highlighted the need for an efficient control procedure for the highly toxic dioxin. The concomitant formation of the dioxin and the trichlorophenol during hydrolysis of sym-tetrachlorobenzene has lead to demands for restrictions on the use of 2,4,5-T and related herbicides. An environmental hazard is also presented by pentachlorophenol which includes the more highly chlorinated dioxins, is particular octachlorodibenzo-p-dioxin (OCDD). The use of pholychlorophenol formulations has been banned in Sweden on the grounds that heat-stable chlorodioxins are formed during incineration; this also points to the need for degradation by chemical means. Dehalogenation of polychlorodibenzodioxins (PCDD) can be accomplished by photolysis in laboratory conditions, but material adsorbed on soil is little affected. Cleavage of the ether linkages with the formation of halophenols may be achieved by treatment with strong acids or quaternary ammonium salts. The dibenzodioxin nucleus, is however, rather resistant to chemical attack and in the absence of a suitable control procedure the use of 2,4,5-T has been restricted in the US by the Environmental Protection Agency. I now report the oxidative degeneration of TCDD and related compounds by ruthenium tetroxide.